Carbonic diesters are compounds of value as automotive gas additives and organic solvents or as reactants, replacing phosgene, in the production of various carbonates, carbamates, urethanes and fine chemicals such as drugs and agrochemicals.
For the commercial production of a carbonic diester, generally the corresponding alcohol is allowed to react with phosgene. However, this known technology demands the use of phosgene having a great toxic potential and, moreover, the reaction of the alcohol with phosgene gives rise to a large quantity of hydrochloric acid which is a highly corrosive substance.
Therefore, a technology has been proposed for producing a carbonic diester without the use of phosgene which comprises allowing the corresponding alcohol to react with carbon monoxide and oxygen in the presence of a catalyst. The catalyst used for this purpose can be classified into two major categories, i.e. the palladium catalyst including a compound of palladium as the main catalyst component and the copper catalyst including a compound of copper as the main catalyst component.
The reaction using the palladium catalyst is described in Japanese Patent Publication Nos. 8816/1986 and 43338/1986. According to this technology, a palladium compound as the main catalyst component is used in combination with a copper compound and an alkali metal compound. The reaction conducted in the presence of a copper catalyst is described in Japanese Patent Publication No. 8020/1981. According to this technology, copper halides and the like are used as catalyst. And these reactions mentioned above are conducted in a liquid phase at a high pressure.
However, since the reaction liquid medium containing such a catalyst, irrespective of whether it is a palladium catalyst or a copper catalyst, is highly corrosive, the reaction must be conducted in a pressure-resistant reactor having an anticorrosive lining made of e.g. glass or a baked-on type enamel. Therefore, since there is an upper limit to the size of a pressure-resistant reactor having such an anticorrosive lining that can be fabricated, it is difficult to produce a carbonic diester containing such a catalyst on a commercial scale.
To obviate this corrosion problem associated with a liquid-phase reaction, a technology has been proposed for producing a carbonic diester which comprises allowing the corresponding alcohol to react with carbon monoxide and oxygen in a gas phase in the presence of a solid catalyst. For example, JP-A-503460/1988 corresponding to WO87/07601 discloses a production process which comprises allowing all the reactants to react in a gas phase using a catalyst comprising cupric chloride supported on a solid support by an impregnation technique.
This technology, however, has a disadvantage that the catalyst tends to be deteriorated since chlorine is eliminated from the catalyst in the course of the reaction. In other words, since the reaction of producing a carbonic diester which comprises allowing an alcohol to react with carbon monoxide and oxygen is a redox reaction, the valency of copper transfers between monovalent and divalent. Therefore, when cupric chloride is used as a catalyst component, chlorine is liable to be eliminated from the catalytic system corresponding to the equilibrium between cations and anions. Further, the technology has a drawback that atacamite [Cu.sub.2 (OH).sub.3 Cl] is produced by reacting by-product water with copper chloride, and an excess amount of chlorine is eliminated from the system and the deterioration of the catalyst is enhanced. Additionally, according to this technology, a highly anti-corrosive reactor is still required, since chloride eliminated from the system causes the corrosion of the equipment. Meanwhile, in the above-mentioned literature, a method of regenerating the catalyst in order to supply the eliminated amount of chlorine to the system is proposed. The corrosion of the reactor, however, is still a disadvantage of the technology, because hydrogen chloride is used in the regeneration of the catalyst.
In these technologies for producing a carbonic diester, irrespective of whether it is a liquid phase reaction or a gas-phase reaction, there are the corrosion of the equipments and the deterioration of the catalysts and these drawbacks add up to a considerable disadvantage in the mass production of a carbonic diester.